The prior art in this field is generally concerned with minimization of network latency. Most of the prior art relates to transmission of multimedia through wired networks, and does not consider that in wireless broadcast applications, imposition of delay through channel coding, or retransmit delay, is both feasible and necessary.
In known multi-stream multimedia play back systems, where the streams are output on different types of devices, playing the same set of streams on different output devices requires the use of a single transmission media. The use of different transmission media, which may include multiple hops over wireless media, as well as multiple hops over wired media, is not considered. The use of different transmission media may be of particular relevance to home and small office networks, where repeaters may be used to account for uncertain propagation conditions within the home/small office. The prior art does not consider networks in which a multimedia stream, because of quality-of-signal (QoS), or capacity limitations, may have different transmission rates at different points in the network. Furthermore, the use of wired/wireless media implies that different delays imposed by coding may be needed. The prior art does not consider networks in which multiple streams can arise from different physical locations in the network with different delays, which might occur within certain ad-hoc networks; and the prior art does not consider that a priori network information may be exploited so that new devices may “join” the network mid-transmission.
U.S. Pat. No. 5,617,539, for “Multimedia collaboration system with separate data network and A/V network controlled by information transmitting on the data network,” to Ludwig et al., granted Apr. 1, 1997, describes a system that integrates real-time and asynchronous networks. This system, however, does not address the wired/wireless synchronization issue, nor does it address the multi-hop wireless synchronization issue.
U.S. Pat. No. 5,623,483, for “Synchronization System for Networked Multimedia Streams,” to Agrawal et al., granted Apr. 22, 1997, discusses multi-stream multimedia content which is played on different output devices and how, with the use of buffers, two disparate multimedia streams may be synchronized to each other.
U.S. Pat. No. 5,689,641, for “Multimedia collaboration system arrangement for routing compressed AV signal through a participant site without decompressing the AV signal,” to Ludwig et al., granted Nov. 18, 1997, further describes the system of U.S. Pat. No. 5,617,539.
U.S. Pat. No. 5,790,792, for “Method and apparatus for transmitting multimedia from an application logic server to interactive multimedia workstations,” to Dudgeon et al., granted Aug. 4, 1998, describes a network wherein a server handles all processing of real-time graphical images, however, this reference does not consider synchronization or wireless issues.
U.S. Pat. No. 5,754,241, for “Video decoder capable of controlling encoded video dat,” to Okada et al., granted May 19, 1998, describes an MPEG decoder having an over-flow proof buffer.
U.S. Pat. No. 5,754,961, for “Radio communication system including SDL having transmission rate of relatively high speed,” to Serizawa et al., granted May 19, 1998, describes a system having both high and low speed transmission/reception capabilities.
U.S. Pat. No. 5,757,857, for “High speed self-adjusting clock recovery circuit with frequency detection,” to Buchwald, granted May 26, 1998, describes a circuit wherein all transmission is done without any systemic phase offset.
U.S. Pat. No. 5,758,079, for “Call control in video conferencing allowing acceptance and identification of participants in a new incoming call during an active teleconference,” to Ludwig et al., granted May 26, 1998, is related to U.S. Pat. No. 5,689,641, discussed above. This reference continues the discussion of synchronization of real-time and asynchronous networks, but still fails to address the issue of wired/wireless packet data synchronization.
U.S. Pat. No. 5,768,321, for “Automatic frequency control unit which detects a frame pattern in a phase modulation signal,” to Watanabe et al., granted Jun. 16, 1998, describes the transmission of a multimedia signal by a satellite communications system.
U.S. Pat. No. 5,777,612, for “Multimedia dynamic synchronization system,” to Kataoke, granted Jul. 7, 1998, describes a multimedia system which allows a user to output synchronized multimedia information starting at a point other than the beginning of a data stream.
U.S. Pat. No. 5,778,191, for “Method and device for error control of a macroblock-based video compression technique,” to Levine et al., granted Jul. 7, 1998, describes application of a fixed length packet synchronization system to variable length data.
U.S. Pat. No. 5,790,533, for “Method and apparatus for adaptive RF power control of cable access units,” to Burke et al., granted Aug. 4, 1998, describes the use of adaptive RF control of data transmission from a device, such as an A/V receiver, attached to a communications network.
U.S. Pat. No. 5,802,294, for “Teleconferencing system in which location video mosaic generator sends combined local participants images to second location video mosaic generator for displaying combined images,” to Ludwig et al., granted Sep. 1, 1998, is a continuation of U.S. Pat. No. 5,689,641, discussed above.
U.S. Pat. No. 5,809,075, for “High speed communications system for analog subscriber connections,” to Townshend, granted Sep. 15, 1998, describes a system using pulse code modulation to achieve relatively high transmission rates over conventional telephone lines.
U.S. Pat. No. 5,809,454, for “Audio reproducing apparatus having voice speed converting function,” to Okada et al., granted Sep. 15, 1998, describes a system for increasing the transmission rate of voice data, while maintaining the normal pitch of the speaker's voice.
U.S. Pat. No. 5,815,634, for “Stream synchronization method and apparatus for MPEG playback system,” to Daum et al., granted Sep. 29, 1998, describes a system for pausing or freeze-framing an audio visual presentation wherein the sound is muted when the picture is stopped, and wherein the sound and picture are substantially synchronized when playback resumes. This reference does not address the technology as applied to a wireless/wired interface.
U.S. Pat. No. 5,818,906, for “Connection event reporting in a cable telephony system,” to Grau et al., granted Oct. 6, 1998, describes a system wherein events which occur on the communication system are logged, and information about the type and frequency of connections made available for network management.
U.S. Pat. No. 5,828,866, for “Real-time synchronization of concurrent views among a plurality of existing applications,” to Hao, et al., granted Oct. 27, 1998, describes a system for synchronizing multiple applications located and operating on multiple processors.
U.S. Pat. No. 5,832,088, for “Method and apparatus for preventing data copying from a disk using data lengths too large for a pirate medium,” to Nakajima et al., granted Nov. 3, 1998 describes a system for preventing the recording of data by an unauthorized entity.
U.S. Pat. No. 5,832,218, for “Client/server electronic mail system for providing off-line client utilization and seamless server resynchronization,” to Gibbs et al., granted Nov. 3, 1998, describes a system for synchronizing an EMail server to a client.
U.S. Pat. No. 5,841,482, for “Transition aligned video synchronization system,” to Wang et al., granted Nov. 24, 1998, describes the insertion of delay signals into an A/V signal without the use of a phase locked loop.
U.S. Pat. No. 5,854,799, for “Video decoder with functions to detect and process errors in encoded video data,” to Okada et al., granted Dec. 29, 1998, describes the replacement of an error-carrying macroblock with an error-free macroblock from a previous frame.
U.S. Pat. No. 5,854,893, for “System for teleconferencing in which collaboration types and participants by names or icons are selected by a participant of the teleconference,” to Ludwig et al., granted Dec. 29, 1998, is a continuation of U.S. Pat. No. 5,689,641, discussed above, and relates to a teleconferencing system wherein the current participants control entry of new participants into the conference.
U.S. Pat. No. 5,857,201, for “Enterprise connectivity to handheld devices,” to Wright, Jr. et al., granted Jan. 5, 1999, describes a system wherein a variety of devices may be connected to a central server regardless of the devices' operating system.
U.S. Pat. No. 5,862,451, for “Channel quality management in a cable telephony system,” to Grau et al., granted Jan. 19, 1999, describes a system wherein, upon initiation of a link by a user, and upon location of a busy channel that the link is intended to traverse, an idle channel is queried to determine if the idle channel is of sufficient quality to complete the link.
U.S. Pat. No. 5,867,654, for “Two monitor videoconferencing hardware,” to Ludwig et al., granted Feb. 2, 1999, is related to U.S. Pat. No. 5,689,641, and describes the use of two monitors in a videoconferencing system.
U.S. Pat. No. 5,884,039, for “System for providing a directory of AV devices and capabilities and call processing such that each participant participates to the extent of capabilities available,” to Ludwig et al., granted Mar. 16, 1999, is related to U.S. Pat. No. 5,689,641, and describes limiting the implementation to a least common denominator.
U.S. Pat. No. 5,886,734, for “Apparatus and method for storage and playback of video images and audio messages in multipoint videoconferencing,” to Ozone et al., granted Mar. 23, 1999, describes a video conferencing “hold” button. The reference does not address the issue of wireless/wired networks.